A shim system of this kind is known, for example, from CN 104865544 A from WUHAN ZHONGKE MR TECHNOLOGY CO LTD (=reference [1]) and from U.S. Pat. No. 3,735,306 A or DE 21 52 006 C2 from VARIAN ASSOCIATES, INC. (=reference [2]).
NMR methods are used to analyze sample compositions or to determine the structure of materials in samples. NMR spectroscopy is an efficient method of instrumental analysis. In such NMR methods, the sample is exposed to a strong static magnetic field B0 in a Z direction, and, in addition, orthogonal high-frequency electromagnetic pulses are irradiated into the sample in the X or Y direction. This results in an interaction with the nuclear spin of the sample material. The development of this nuclear spin of the sample over time in turn produces high-frequency electromagnetic fields, which are detected in the NMR apparatus. Information regarding the properties of the sample can be obtained from the detected HF fields. In particular, the chemical bonding behaviors in the sample can be inferred from the position and intensity of NMR lines.
The homogeneity of the strong static magnetic field B0 in the Z direction is decisive for the quality of the measurement. Complex coil systems are used to influence and homogenize the magnetic field of an NMR system, and are known as shim systems.
FIG. 1 shows a simplified shim system according to the existing conventional art. The figure shows only the partial coils that influence the static magnetic field B0 in the Z direction.
The production of the partial coils and the connections of these partial coils to the terminal unit takes place on winding machines. For this purpose, the coil former, the extension tube and parts of the connection unit are assembled in advance and this pre-assembled unit is clamped on the winding machine.
The winding then takes place such that a wire is fixed to the terminal unit as a connection line and is guided therefrom along and in longitudinal grooves of the extension tube and of the coil former as far as the first peripheral groove of the first partial coil, which groove is the most remote from the terminal unit. This partial coil is then wound using the same wire. This same wire, again as a connection line, is then guided back in the same manner to the terminal unit and fixed there.
Following this, the further partial coils are produced in the same manner. The terminal lines to the foregoing partial coils come to lie under the further partial coils.
The process is made more complicated if two non-adjacent partial coils have to be connected in series. In this case, the first of the two partial coils firstly has to be wound as previously described. The terminal line is then guided back, but not as far as the terminal unit; instead, the wire reel, from which the wire for the terminal line is unwound, provisionally has to be fixed near the terminal unit such that, when the following partial coils are being wound, it turns therewith but is not unwound further. The partial coils which are located between the partial coils to be connected in series are then produced. Following this, the wire reel is re-received and the second of the coils connected in series is wound and the wire is then guided to and fixed to the terminal unit as a terminal line. If two partial coils connected in series obtain a different polarity, the two partial coils have to be mounted in different winding directions.
This is disadvantageous in that this procedure is so complicated that this production process can no longer be automated with reasonable effort.
Shim coils that are produced according to the conventional teachings described above are also disadvantageous in that the coil former already has to be connected to the extension tube before the time-consuming winding process. Since there are extension tubes of lengths that differ depending on the required length of the shim system, it therefore already has to be definitively decided at that point what shim system length should be made.
It is currently not possible to make-to-stock the time-consuming windings of the partial coils in advance. In such a case, it would be possible to produce a shim coil much more rapidly after receiving an order because then only a coil former already equipped with its partial coils would have to be fitted with the correct extension tube and the remaining parts. Instead, only a complex manual production in the manner described above is possible according to the conventional teachings.